1. Field of the Invention
Embodiments of the present invention relate in general to the combined use of laser therapy and laser light absorbing agents in the treatment of skin conditions associated with the production of sebum by sebaceous glands. More particularly, embodiments of the present invention relate to methods of preventing, reducing, eliminating, or otherwise treating unwanted skin conditions, such as acne, using laser light and one or more exogenous chromophores to disrupt production of sebum without significant harm to surrounding normal tissue.
2. Description of Related Art
Unwanted skin conditions associated with the production or overproduction of sebum are well known. One example of such an unwanted skin condition includes common acne which is a major treatment concern of many dermatologists. It is estimated that as many as 32 million Americans exhibit some form of unwanted acne.
The treatment of acne is of major concern to dermatologists. Acne accounts for more than four million visits to dermatologists each year. Typically, acne arises in the early teen years and subsides by the mid twenties. In many cases, particularly in women, acne remains a chronic problem well into the adult years. It is estimated that as many as 32 million Americans suffer from acne.
Acne vulgaris, the most common form of acne, is the result of the secretion of sebum by the sebaceous gland into a blocked pore. Continued secretion results in buildup of the sebum in the blocked pore. Bacteria in the pore gives rise to infection and a common unsightly skin condition known as pimples. Sebaceous gland hyperplasia is also a common form of acne in which the sebaceous gland grows or become enlarged as a result of overproduction of sebum. A pimple is formed even if the gland is not blocked.
Sebaceous glands and the sebum they produce apparently have no commonly accepted significant function in humans. The skin of young children does not appear to be negatively affected by the almost total lack of sebum. The only known role of sebum in humans is in the pathogenesis of acne. In the past, physicians treated acne with radiation therapy to destroy the sebaceous gland. Radiation, however, does not specifically target the sebaceous glands, and can cause significant morbidity to normal tissue because of its mutagenic toxicity. Increased risk of cutaneous carcinoma has also been associated with radiation therapy. Current acne treatments do not eradicate the sebaceous glands selectively and without harm to surrounding normal tissue, and therefore remain non-curative and inadequate. The result is years of chronic therapy and potential scarring for the patient.
Selective photothermolysis is a method of causing selective and irreversible photothermal damage to tissue structures containing a chromophore that can be used to distinguish that target structure from surrounding tissue. For a light source, typically a laser, to be useful for selective photothermolysis, it must emit with sufficient intensity at a wavelength preferentially absorbed by the target chromophore. The pulse duration or exposure time of the source must be less than the thermal relaxation time of the target to minimize temperature increases in tissue surrounding the target. Techniques based on this concept using well known laser systems are well established for treatment of benign cutaneous vascular lesions such as portwine stain (PWS), birthmarks, telangiectasias, hemangiomas, warts, psoriasis, arthritis in which hemoglobin in the abnormal ectatic lesional vasculature serves as the chromophore and the target is the vessel wall, as well as, atherosclerotic plaque and other desired applications. See U.S. Pat. No. 5,312,395; U.S. Pat. No. 5,749,868; U.S. Pat. No. 5,257,970; U.S. Pat. No. 5,066,293, U.S. Pat. No. 5,346,488, “Selective Photothermolysis: Precise Microsurgery by Selective Absorption of Pulsed Radiation”, Anderson et al., Science, 220:524-527 (1983); Spears et al. J. Clin. Invest, 71, 39-399 (1983), the disclosure of each of which is hereby incorporated by reference in their entireties for all purposes. The deepest blood vessels contributing to the color of PWS lesions are approximately 1 mm below the skin surface, and are accessible to selective photothermal targeting using available lasers such as the 585 nm pulsed dye laser. The theoretical advantages of selective photothermolysis have been borne out in clinical studies showing that PDL (pulsed dye laser) treatment of benign cutaneous vascular lesions is associated with very low risk of scarring. However, photothermolysis techniques involving the direction of laser light onto the surface of skin would be more effective if the laser light was not substantially absorbed by components of skin and particularly if an exogenous chromophore was used which selectively collected in the targeted tissue and which absorbed laser light at a wavelength substantially outside that absorbed by normal skin components.
One approach to the treatment of acne is to reduce the production of sebum by disrupting or even destroying the sebaceous gland. One such method described in U.S. Pat. No. 5,817,089 includes forcing, for example by the use of ultrasound, an exogenous chromophore into spaces within or adjacent sebaceous glands. The chromophore is then illuminated with short pulses of laser light so as to provide sufficient energy to the chromophore to create explosions which blow off layers of dead skin cells and/or destroy tissue responsible for hair growth and/or sebum production.
The use of beta-carotene as an exogenous chromophore along with lasers to treat acne is considered in U.S. Pat. No. 5,304,170. However, the laser light has a wavelength between 425 nm and 550 nm which suffers from poor penetration within the tissues. Further, while beta-carotene does collect in sebaceous glands, it also collects in the tissue between the glands and surrounding tissue and skin components, resulting in poor selectivity and yellowing of the skin.
Efforts to use lasers to treat certain skin conditions and to effect hair removal include Manuskiatti et al., J. Am. Acad. Dermatol., vol. 41, Number 2, Part 1, pp. 176-180 (1999), Friedlander, Pediatric Dermatology, vol. 15, No. 5, pp. 396-398 (1998), Shuster, Acta Dermatovener (Stockh) Suppl., 120, pp. 43-46, Sigurdsson et al., Dermatology, 194, pp. 256-260 (1997), Sumian et al., J. Am. Acad. Dermatol., Vol. 41, Number 2, Part 1, pp. 172-175 (1999), the disclosure of each of which is hereby incorporated by reference in their entireties for all purposes. However, these efforts do not recognize the use of laser light having a wavelength outside that significantly absorbed by skin or skin components or the use of an exogenous chromophore which can be selectively introduced to sebaceous glands.
Accordingly, there is a need in the art to provide methods of treating unwanted skin conditions associated with sebum production or overproduction which employ laser light having a wavelength outside that substantially absorbed by skin or skin components. There is also a further need in the art to selectively localize the effects of photothermolysis to sebaceous glands using a chromophore which absorbs laser light having a wavelength outside that substantially absorbed by skin or skin components and further without significantly harming surrounding normal tissue. There is a further need to develop methods for introducing an exogenous chromophore into sebaceous glands where such chromophore would normally lack affinity for sebaceous gland material.